java.lang.NoClassDefFoundError and java.lang.NoSuchMethodError in UNIX
By: Yolander
Exception in thread "main"
java.lang.NoClassDefFoundError: HelloWorldApp
If you receive this error, java
cannot find your bytecode
file, HelloWorldApp.class
.
One of the places java
tries to find your bytecode file is
your current directory. So, for example, if your bytecode file is in /home/jdoe/java
,
you should change your current directory to that. To change your directory,
type the following command at the prompt and press Return:
cd /home/jdoe/java
If you enter pwd
at the prompt, you should see /home/jdoe/java
.
If you enter ls
at the prompt, you should see your .java
and .class
files. Now enter java HelloWorldApp
again.
If you still have problems, you might have to change your CLASSPATH environment variable. To see if this is necessary, try clobbering the classpath with the following command.
unset CLASSPATH
Now enter java HelloWorldApp
again. If the program works now,
you'll have to change your CLASSPATH variable in the same manner as the PATH
variable above.
Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorldApp/class
A common mistake made by beginner programmers is to try and run the
java
launcher on the.class
file that was created by the compiler. For example, you'll get this error if you try to run your program withjava HelloWorldApp.class
instead ofjava HelloWorldApp
. Remember, the argument is the name of the class that you want to use, not the filename.
Exception in thread "main" java.lang.NoSuchMethodError: main
The Java VM requires that the class you execute with it have a
main
method at which to begin execution of your application.
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